This invention relates to a method of cooling an engine for an automobile, in particular to a method of operating a cooling system having a variable coolant flow control valve.
In a typical motor vehicle cooling circuit, coolant passes through a jacket surrounding the vehicle engine and its temperature rises. It then passes through the radiator, entering the radiator through a manifold and then passing through cooling tubes where air flows over the tubes to remove heat from and to reduce the temperature of the coolant before the coolant is re-circulated via a second manifold to the vehicle engine.
Cooling systems generally have a coolant pump for pumping coolant through the engine coolant circuit. A valve is conventionally provided to prevent coolant circulating through the radiator whilst the engine is warming up. The cooling system usually includes a fan for blowing air over the radiator in the event that the coolant becomes too hot when the speed of the automobile does not provide the necessary cooling air flow over the radiator.
Known methods of cooling engines usually include controls based on output of a thermostatic device for opening and closing the valve and for switching the fan on and off. The speed of the water pump is generally operated in dependence upon the engine speed.
The problem with such known systems is that it is difficult to operate the engine at calibratable optimum temperatures, and thus fuel consumption, power consumption and emissions are worse than optimum.
This invention seeks to alleviate the aforementioned problems.
According to the present invention there is provided a method of controlling an engine cooling system for an automobile, the cooling system comprising a variable coolant flow control valve for controlling the amount of coolant direct to the heat exchanger; the method comprising the steps: measuring the temperature of the engine; comparing the measured temperature to a desired operating temperature to generate an error value and opening the valve by a variable amount according to the error value when the error value is within a range determined by a first predetermined threshold and a second predetermined threshold.
Preferably the method further comprises the steps of: fully opening the valve when the error value is outside said range and the measured temperature is greater than the desired temperature; and fully closing the valve when the error value is outside said range and the measured temperature is less than the desired temperature.
In a preferred embodiment the cooling system further comprises a variable speed fan, and the method further comprises the step of controlling the fan in accordance with a measured air speed across the heat exchanger when the measured temperature is greater than a predetermined fan-on threshold. It is an advantage if the step of controlling the fan in accordance with a measured air speed across the heat exchanger is continued until the measured temperature is less than or equal to the desired temperature, this introduces hysteresis, to avoid the fan switching on and off too frequently.
In a cooling system including an air conditioner the method further comprises the step of operating the fan in accordance with a measured air conditioning demand.
It is a further advantage if the fan is operated in accordance with a measured ambient temperature and if fan is switched off when the vehicle speed is greater than a predetermined vehicle speed.
In a preferred embodiment the cooling system further comprises a variable speed pump and the method further comprises the step of controlling the speed of the pump according to the error value, a measured engine load and a measured oil temperature.
Preferably stored data records relationships between pump speed and each of the error value, the measured engine load and the measured oil temperature, and in which the controlling step comprises selecting the highest pump speed according to any one of the relationships when the measured temperature is greater than the desired temperature; and selecting the lowest pump speed according to any one of the relationships otherwise.
In a preferred embodiment the engine operates in a warm up mode, an economy mode, a power mode or a cool down mode, and in which the desired operating temperature is dependent upon the mode in which the engine is operating.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.